1. Technical Field
The present invention relates to a wet-processing apparatus which processes substrates, such as semiconductor wafers or glass panels for liquid crystal displays (LCD panels), by spouting processing liquids, such as resist solutions and developers from processing liquid spouting nozzles onto substrates.
2. Description of the Related Art
Generally, a resist pattern forming method, namely, one of methods of fabricating semiconductor devices and LCD panels, forms a resist pattern on a substrate or a semiconductor wafer (hereinafter referred to simply as “wafer”) by a series of processes for forming a resist film on the wafer, and developing the resist film exposed through a photomask. Usually, the series of processes are carried out by a coating and developing apparatus.
The coating and developing apparatus is provided with wet-processing units including coating units for resist solution application, and developing units for processing a wafer processed by an exposure process by a developing process. The coating units and the developing units are used to attain a high throughput.
A coating unit for coating a wafer with, for example, a resist solution has a spin chuck, namely, a substrate holder, and a splash cup surrounding the spin chuck. The resist solution is spouted onto a substantially central part of a wafer held by the spin chuck. The spin chuck is rotated for spin coating and centrifugal drying. The wafer coated with the resist solution is subjected to side rinsing.
Since most resist solutions used as coating liquids are expensive, it is desired to reduce the amount of the resist solution necessary for coating a wafer to the least possible extent. For example, it is required to coat a 300 mm-diameter substrate with not more than 1 cm3 of the resist solution. Since such a small amount of the resist solution is spouted in a short time, it is difficult to measure the amount of the spouted resist solution by a flowmeter. A recent coating and developing apparatus is built so as to occupy a small floor space and the component units thereof are stacked vertically in layers. Consequently, only small spaces are available for maintenance work and visual inspection. It is difficult to perceive failure in spouting the resist solution and faulty resist solution spouting under such severe spatial and operational conditions. If the perception of such an abnormal processing condition is delayed, it is possible that a large amount of unacceptable substrates are produced by defective processes.
A technique to cope with such a problem is proposed in JP-A 2008-135679 (Patent document 1). This technique illuminates the tip of a nozzle with light emitted by a light source, such as an LED lamp, forms an image of the tip of the nozzle by a camera to obtain image data on the tip of the nozzle, and analyzes the image data to find out a faulty condition, such as the dripping of the coating liquid from the nozzle.